Effects of Nb2O5 Replacement by Er2O3 on elastic and structural properties of 75TeO2–(10 − x)Nb2O5–15ZnO–(x)Er2O3 glass

Abstract

Tellurite 75TeO2–(10−x)Nb2O5–15ZnO–(x)Er2O3; (x=0.0–2.5mol%) glass system with concurrent reduction of Nb2O5 and Er2O3 addition have been prepared by melt-quenching method. Elastic properties together with structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo-overlap technique at 5MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at x=0.5mol% but remained constant between x=1.0mol% to x=2.0mol%, before increasing back with Er2O3 addition at x=2.5mol%. The initial drop in shear velocity and related elastic moduli observed at x=0.5mol% were suggested to be due to weakening of glass network rigidity as a result of increase in non-bridging oxygen (NBO) ions as a consequence of Nb2O5 reduction. The near constant values of shear velocity, elastic moduli, Debye temperature, hardness and Poisson's ratio between x=0.5mol% to x=2.0mol% were suggested to be due to competition between bridging oxygen (BO) and NBO ions in the glass network as Er2O3 gradually compensated for Nb2O5. Further addition of Er2O3 (x>2.0mol%) seems to further reduce NBO leading to improved rigidity of the glass network causing a large increase of ultrasonic velocity (vL and vS) and related elastic moduli at x=2.5mol%. FTIR analysis on NbO6 octahedral, TeO4 trigonal bipyramid (tbp) and TeO3 trigonal pyramid (tp) absorption peaks confirmed the initial formation of NBO ions at x=0.5mol% followed by NBO/BO competition at x=0.5–2.0mol%. Appearance of ZnO4 tetrahedra and increase in intensity of TeO4 tbp absorption peaks at x=2.0mol% and x=2.5mol% indicate increase in formation of BO.